8,515 research outputs found
Kondo Effect in a Quantum Antidot
We report Kondo-like behaviour in a quantum antidot (a submicron depleted
region in a two-dimensional electron gas) in the quantum-Hall regime. When both
spin branches of the lowest Landau level encircle the antidot in a magnetic
field ( T), extra resonances occur between extended edge states via
antidot bound states when tunnelling is Coulomb blockaded. These resonances
appear only in alternating Coulomb-blockaded regions, and become suppressed
when the temperature or source-drain bias is raised. Although the exact
mechanism is unknown, we believe that Kondo-like correlated tunnelling arises
from skyrmion-type edge reconstruction. This observation demonstrates the
generality of the Kondo phenomenon.Comment: 9 pages, 3 figures (Fig.3 in colour), to appear in Phys. Rev. Let
Phonon emission and arrival times of electrons from a single-electron source
In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy
Dynamics and High Energy Emission of the Flaring HST-1 Knot in the M 87 Jet
Stimulated by recent observations of a radio-to-X-ray synchrotron flare from
HST-1, the innermost knot of the M 87 jet, as well as by a detection of a very
high energy gamma-ray emission from M 87, we investigated the dynamics and
multiwavelength emission of the HST-1 region. We study thermal pressure of the
hot interstellar medium in M 87 and argue for a presence of a gaseous
condensation in its central parts. Interaction of the jet with such a feature
is likely to result in formation of a converging reconfinement shock in the
innermost parts of the M 87 jet. We show that for a realistic set of the
outflow parameters, a stationary and a flaring part of the HST-1 knot located
\~100 pc away from the active center can be associated with the decelerated
portion of the jet matter placed immediately downstream of the point where the
reconfinement shock reaches the jet axis. We discuss a possible scenario
explaining a broad-band brightening of the HST-1 region related to the variable
activity of the central core. We show that assuming a previous epoch of the
high central black hole activity resulting in ejection of excess particles and
photons down along the jet, one may first expect a high-energy flare of HST-1
due to inverse-Comptonisation of the nuclear radiation, followed after a few
years by an increase in the synchrotron continuum of this region. If this is
the case, then the recently observed increase in the knot luminosity in all
spectral bands could be regarded as an unusual echo of the outburst that had
happened previously in the active core of the M 87 radio galaxy.Comment: 30 pages, 7 figures included. Accepted for publication in MNRA
ALMA polarimetric studies of rotating jet/disk systems
We have recently obtained polarimetric data at mm wavelengths with ALMA for
the young systems DG Tau and CW Tau, for which the rotation properties of jet
and disk have been investigated in previous high angular resolution studies.
The motivation was to test the models of magneto-centrifugal launch of jets via
the determination of the magnetic configuration at the disk surface. The
analysis of these data, however, reveals that self-scattering of dust thermal
radiation dominates the polarization pattern. It is shown that even if no
information on the magnetic field can be derived in this case, the polarization
data are a powerful tool for the diagnostics of the properties and the
evolution of dust in protoplanetary disks.Comment: 9 pages, 3 figures, to appear in "Jet Simulations, Experiments and
Theory. Ten years after JETSET, what is next ?", C. Sauty ed., Springer
Natur
Coulomb blockade of tunnelling through compressible rings formed around an antidot: an explanation for Aharonov-Bohm oscillations
We consider single-electron tunnelling through antidot states using a
Coulomb-blockade model, and give an explanation for h/2e Aharonov-Bohm
oscillations, which are observed experimentally when the two spins of the
lowest Landau level form bound states. We show that the edge channels may
contain compressible regions, and using simple electrostatics, that the
resonance through the outer spin states should occur twice per h/e period. An
antidot may be a powerful tool for investigating quantum Hall edge states in
general, and the interplay of spin and charging effects that occurs in quantum
dots.Comment: 5 pages, 4 Postscript figure
Galactic-Center Hyper-Shell Model for the North Polar Spurs
The bipolar-hyper shell (BHS) model for the North Polar Spurs (NPS-E, -W, and
Loop I) and counter southern spurs (SPS-E and -W) is revisited based on
numerical hydrodynamical simulations. Propagations of shock waves produced by
energetic explosive events in the Galactic Center are examined. Distributions
of soft X-ray brightness on the sky at 0.25, 0.7, and 1.5 keV in a +/-50 deg x
+/-50 deg region around the Galactic Center are modeled by thermal emission
from high-temperature plasma in the shock-compressed shell considering
shadowing by the interstellar HI and H2 gases. The result is compared with the
ROSAT wide field X-ray images in R2, 4 and 6 bands. The NPS and southern spurs
are well reproduced by the simulation as shadowed dumbbell-shaped shock waves.
We discuss the origin and energetics of the event in relation to the starburst
and/or AGN activities in the Galactic Center. [ High resolution pdf is
available at http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2016bhs/ ]Comment: 13 pages, 20 figures; To appear in MNRA
A numerical code to study the variability of Blazar emission
We present a numerical code, written in C, which can be used to simulate or
to analyze the emission of Blazars over the entire electromagnetic spectrum.
Our code can reproduce the following features: synchrotron emission, inverse
Compton emission (Thomson Klein-Nishina regime) external Compton emission,
accretion disk variability using a Cellular Automata algorithm, temporal
evolution of the emitting plasma energy distribution, flaring phenomena, light
curves in the rest and in the observer frame (taking account for time crossing
effects). In this paper we will show mainly the accretion disk simulation, and
the implications in the External Compton scenario.Comment: 4 pages, 2 eps figures. Poster to "The Physics of Relativistic Jets
in the CHANDRA and XMM Era" (Bologna CNR). Proceedings to be published in New
Astronomy Review
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